1. Technical Field
The invention generally relates to the focusing of images captured by cameras.
2. Related Art
Various auto-focus techniques have been developed to provide in-focus camera images. In one such technique, a digital camera lens may be translated to various incremental positions at different distances from an image sensor. The image sensor captures an image at each incremental position while the lens remains stationary. A sharpness filter may be applied to each image to provide an associated sharpness score for each image. The lens position associated with the highest sharpness score may then be used for capturing in-focus images.
Unfortunately, this approach can sometimes be problematic for fine-grained incremental changes between lens positions. In such cases, images taken at adjacent or nearby positions may exhibit little difference from each other. Consequently, their associated sharpness scores may also exhibit very little difference. As a result, it can become difficult for a processor performing an auto-focus process to clearly identify a preferred lens position associated with an in-focus image over other lens positions associated with slightly out-of-focus images. Moreover, if there is little difference between the images in a given range, the processor may take longer and consume excessive processor resources to analyze a potentially large number of similar images in the range.
Although various non-linear functions (e.g., Sobel filters or Laplacian filters) may be used in an attempt to further distinguish between similar images, such functions are typically computationally-intensive and therefore require additional time and/or additional processor resources. Such implementations can accordingly increase the cost and decrease the overall efficiency of the auto-focus process.